Libevent prior 2.2.2-alpha WebSocket Server ws.c buffer overflow

Summaryinfo

A vulnerability has been found in Libevent prior 2.2.2-alpha and classified as problematic. This impacts an unknown function of the file ws.c of the component WebSocket Server. The manipulation leads to buffer overflow. This vulnerability is traded as CVE-2026-63495. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in Libevent prior 2.2.2-alpha and classified as problematic. This issue affects an unknown part of the file ws.c of the component WebSocket Server. The manipulation with an unknown input leads to a buffer overflow vulnerability. Using CWE to declare the problem leads to CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. Impacted is availability. The summary by CVE is:

Libevent is an event notification library. From 2.2.0-alpha-dev until 2.2.2-alpha, the libevent WebSocket server in ws.c accumulates fragmented frames in evws->incomplete_frames without enforcing a total message-size limit. An unauthenticated remote client can repeatedly send fragmented WebSocket frames below WS_MAX_RECV_FRAME_SZ with FIN=0, causing the evbuffer to grow without bound until the process or host exhausts memory. This issue is fixed in version 2.2.2-alpha.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-63495 since 07/16/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 08/20/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Name

• Libevent

Version

• < 2.2.2-alpha

Website

• Product: https://github.com/libevent/libevent/

CPE 2.3info

• 🔒

CPE 2.2info

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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